Gas turbine combustor and operating method thereof

ABSTRACT

A gas turbine combustor has a combustion chamber into which fuel and air are supplied, wherein the fuel and the air are supplied into said combustion chamber as a plurality of coaxial jets.

[0001] This is a continuation-in-part (CIP) application of U.S. Ser. No.10/083,360 filed Feb. 27, 2002, now pending, the entire disclosure ofwhich is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a gas turbine combustor and anoperating method thereof.

[0004] 2. Description of Prior Art

[0005] The present invention specifically relates to a low NOx type gasturbine combustor which emits low levels of nitrogen oxides. The priorart has been disclosed in Japanese Application Patent Laid-OpenPublication No. Hei 05-172331.

[0006] In a gas turbine combustor, since the turndown ratio from startupto the rated load condition is large, a diffusing combustion systemwhich directly injects fuel into a combustion chamber has been widelyemployed so as to ensure combustion stability in a wide area. Also, apremixed combustion system has been made available.

[0007] In said prior art technology, a diffusing combustion system has aproblem of high level NOx. A premixed combustion system also hasproblems of combustion stability, such as flash back, and flamestabilization during the startup operation and partial loadingoperation. In actual operation, it is preferable to simultaneously solvethose problems.

SUMMARY OF THE INVENTION

[0008] The main purpose of the present invention is to provide a gasturbine combustor having low level NOx emission and good combustionstability and an operating method thereof.

[0009] The present invention provides a gas turbine combustor having acombustion chamber into which fuel and air are supplied, wherein thefuel and the air are supplied into said combustion chamber as aplurality of coaxial jets.

[0010] Further, a method of operating a gas turbine combustor accordingto the present invention is the method of operating a gas turbinecombustor having a combustion chamber into which fuel and air aresupplied, wherein the fuel and the air are supplied into said combustionchamber as a plurality of coaxial jets.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a diagram, for explanation, including a generalcross-sectional view of a first embodiment according to the presentinvention.

[0012]FIG. 2 is a sectional view, for explanation, of a diffusingcombustion system.

[0013]FIG. 3 is a sectional view, for explanation, of a premixedcombustion system.

[0014]FIG. 4(a) is a sectional view of a nozzle portion of a firstembodiment according to the present invention.

[0015]FIG. 4(b) is a side view of FIG. 4(a).

[0016]FIG. 5(a) is a sectional view, for detailed explanation, of anozzle portion of a second embodiment according to the presentinvention.

[0017]FIG. 5(b) is a side view of FIG. 5(a).

[0018]FIG. 6(a) is a sectional view, for detailed explanation, of anozzle portion of a third embodiment according to the present invention.

[0019]FIG. 6(b) is a side view of FIG. 6(a).

[0020]FIG. 7(a) is a sectional view, for detailed explanation, of anozzle portion of a fourth embodiment according to the presentinvention.

[0021]FIG. 7(b) is a side view of FIG. 7(a).

[0022]FIG. 8(a) is a sectional view, for detailed explanation, of anozzle portion of a fifth embodiment according to the present invention.

[0023]FIG. 8(b) is a side view of FIG. 8(a).

[0024]FIG. 9(a) is a sectional view, for detailed explanation, of anozzle portion of a sixth embodiment according to the present invention.

[0025]FIG. 9(b) is a side view of FIG. 9(a).

[0026]FIG. 10 is a sectional view, for detailed explanation, of a nozzleportion of a seventh embodiment according to the present invention.

[0027]FIG. 11 is a sectional view, for detailed explanation, of a nozzleportion of an eighth embodiment according to the present invention.

[0028]FIG. 12 is a sectional view for detailed explanation of a nozzleportion of a ninth embodiment of the present invention;

[0029]FIG. 13a is a sectional view for detailed explanation of anothernozzle portion of the ninth embodiment of the present invention;

[0030]FIG. 13b is a side view for detailed explanation of a nozzleportion of the ninth embodiment of the present invention;

[0031]FIG. 14 is a sectional view for detailed explanation of a nozzleportion of the ninth embodiment of the present invention;

[0032]FIG. 15 is views for detailed explanation of various nozzleformations of the present invention;

[0033]FIG. 16a is a side view for detailed explanation of a nozzleportion of a tenth embodiment of the present invention;

[0034]FIG. 16b is a side view for detailed explanation of another nozzleportion of the tenth embodiment of the present invention; and

[0035]FIG. 17 is a graphical illustration showing a relationship betweenpremixing distances and NOx emission amounts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] First, two kinds of combustion systems for a gas turbinecombustor will be described.

[0037] (1) In a diffusing combustion system, as shown in FIG. 2, fuel isinjected outward in the vicinity of the outlet of an air swirlerarranged at a combustor head portion so as to intersect with a swirlingair flow, generating a circulating flow on the central axis, therebystabilizing a diffusion flame.

[0038] In FIG. 2, air 50 sent from a compressor 10 passes between anouter casing 2 and a combustor liner 3, and a portion of the air flowsinto a combustion chamber 1 as diluting air 32 which promotes mixture ofcooling air 31 and combustion gas in the combustor liner, and anotherportion of the air flows into the combustion chamber 1 through the airswirler 12 as head portion swirling air 49. Gaseous fuel 16 is injectedoutward from a diffusion fuel nozzle 13 into the combustion chamber 1 soas to intersect with the swirling air flow, and forms a stable diffusionflame 4 together with the head portion swirling air 49 and primarycombustion air 33. Generated high-temperature combustion gas flows intoa turbine 18, performs its work, and then is exhausted.

[0039] The diffusing combustion system shown herein has high combustionstability, while a flame is formed in a area in which fuel and oxygenreach the stoichiometry, causing the flame temperature to rise close tothe adiabatic flame temperature. Since the rate of nitrogen oxideformation exponentially increases as the flame temperature rises,diffusing combustion generally emits high levels of nitrogen oxides,which is not desirable from the aspect of air-pollution control.

[0040] (2) On the other hand, the premixed combustion system is used tolower the level of NOx. FIG. 3 shows an example wherein the centralportion employs diffusing combustion having good combustion stabilityand the outer-periphery side employs premixed combustion having low NOxemission to lower the level of NOx. In FIG. 3, air 50 sent from acompressor 10 passes between an outer casing 2 and a combustor liner 3,and a portion of the air flows into a combustion chamber 1 as coolingair 31 for the combustor liner and combustion gas in the combustorliner, and another portion of the air flows into a premixing chamber 23as premixed combustion air 48. Remaining air flows into the combustionchamber 1, flowing through a passage between the premixing-chamberpassage and the combustor end plate and then through a combustion airhole 14 and a cooling air hole 17. Gaseous fuel 16 for diffusingcombustion is injected into the combustion chamber 1 through a diffusionfuel nozzle 13 to form a stable diffusion flame 4. Premixing gaseousfuel 21 is injected into the annular premixing chamber 23 through a fuelnozzle 8, being mixed with air to become a premixed air fuel mixture 22.This premixed air fuel mixture 22 flows into the combustion chamber 1 toform a premixed flame 5. Generated high-temperature combustion gas issent to a turbine 18, performs its work, and then is exhausted.

[0041] However, if such a premixed combustion system is employed,included instable factors peculiar to premixed combustion may cause aflame to enter the premixing chamber and burn the structure, or causewhat is called a flash back phenomenon to occur.

[0042] In an embodiment according to the present invention, a fuel jetpassage and a combustion air flow passage are disposed on the same axisto form a coaxial jet in which the air flow envelops the fuel flow, andalso disposed on the wall surface of the combustion chamber to formmultihole coaxial jets being arranged such that a large number ofcoaxial jets can be dispersed. Further, this embodiment is arranged suchthat a part of or all of the coaxial jets can flow in with a properswirling angle around the combustor axis. Furthermore, it is arrangedsuch that the fuel supply system is partitioned into a plurality ofsections so that fuel can be supplied to only a part of the systemduring the gas turbine startup operation and partial loading operation.

[0043] In the form of a coaxial jet in which the air flow envelopes thefuel, the fuel flows into the combustion chamber, mixes with an ambientcoaxial air flow to become a premixed air fuel mixture having a properstoichiometric mixture ratio, and then comes in contact with ahigh-temperature gas and starts to burn. Accordingly, low NOx combustionequivalent to lean premixed combustion is possible. At this time, thesection which corresponds to a premixing tube of a conventionalpremixing combustor is extremely short, and the fuel concentrationbecomes almost zero in the vicinity of the wall surface, which keeps thepotential of burnout caused by flash back very low.

[0044] Further, by providing an arrangement such that a part of or allof the coaxial jets flow in with a proper swirling angle around thecombustor axis, in spite of the form of a coaxial jet flow, it ispossible to simultaneously form a recirculating flow to stabilize theflame.

[0045] Furthermore, it is possible to ensure the combustion stability bysupplying fuel to only a part of the system during the gas turbinestartup operation and partial loading operation thereby causing the fuelto become locally over-concentrated and burning the fuel in themechanism similar to the diffusing combustion which utilizes oxygen inthe ambient air.

[0046] First Embodiment

[0047] A first embodiment according to the present invention will bedescribed hereunder with reference to FIG. 1. In FIG. 1, air 50 sentfrom a compressor 10 passes between an outer casing 2 and a combustorliner 3. A portion of the air 50 is flown into a combustion chamber 1 ascooling air 31 for the combustor liner 3. Further, remaining air 50 isflown into the combustion chamber 1 as coaxial air 51 from the interiorof inner cylinder 2 a through an air hole 52.

[0048] Fuel nozzles 55 and 56 are disposed coaxially or almost coaxiallywith combustion air holes 52. Fuel 53 and fuel 54 are injected into acombustion chamber 1 from fuel nozzles 55 and fuel nozzles 56 throughsupply paths 55 a, 56 a as jets almost coaxial with the combustion airthereby forming a stable flame. Generated high-temperature combustiongas is sent to a turbine 18, performs its work, and then is exhausted.

[0049] In this embodiment, with respect to fuel 53 and fuel 54, a fuelsupply system 80 having a control valve 80 a is partitioned. That is,the fuel supply system 80 herein is partitioned into a first fuel supplysystem 54 b and a second fuel supply system 53 b. The first fuel supplysystem 54 b and the second fuel supply system 53 b haveindividually-controllable control valves 53 a and 54 a, respectively.The control valves 53 a and 54 a are arranged such that each valveindividually controls each fuel flow rate according to the gas turbineload. Herein, the control valve 53 a can control the flow rate of a fuelnozzle group 56 in the central portion, and the control valve 54 a cancontrol the flow rate of a fuel nozzle group 55 which is a surroundingfuel nozzle group. This embodiment comprises a plurality of fuel nozzlegroups: a fuel nozzle group in the central portion and a surroundingfuel nozzle group, fuel supply systems corresponding to respective fuelnozzle groups, and a control system which can individually control eachfuel flow rate as mentioned above.

[0050] Next, the nozzle portion will be described in detail withreference to FIGS. 4(a) and 4(b). In this embodiment, the fuel nozzlebody is divided into central fuel nozzles 56 and surrounding fuelnozzles 55. On the forward side of the fuel nozzles 55 and 56 in thedirection of injection, corresponding air holes 52 and 57 are provided.A plurality of air holes 52 and 57 both having a small diameter areprovided on the disciform member 52 a. A plurality of air holes 52 and57 are provided so as to correspond to a plurality of fuel nozzles 55and 56.

[0051] Although the diameter of the air holes 52 and 57 is small, it ispreferable to form the holes in such size that when fuel injected fromthe fuel nozzles 55 and 56 passes through the air holes 52 and 57, afuel jet and an circular flow of the air enveloping the fuel jet can beformed accompanying the ambient air. For example, it is preferable forthe diameter to be a little larger than the diameter of the jet injectedfrom the fuel nozzles 55 and 56.

[0052] The air holes 52 and 57 are disposed to form coaxial jetstogether with the fuel nozzles 55 and 56, and a large number of coaxialjets in which an annular air flow envelopes a fuel jet are injected fromthe end face of the air holes 52 and 57. That is, the fuel holes of thefuel nozzles 55 and 56 are disposed coaxially or almost coaxially withthe air holes 52 and 57, and the fuel jet is injected in the vicinity ofthe center of the inlet of the air holes 52 and 57, thereby causing thefuel jet and the surrounding annular air flow to become a coaxial jet.

[0053] Since fuel and air are arranged to form a large number of smalldiameter coaxial jets, the fuel and air can be mixed at a shortdistance. As a result, there is no mal distribution of fuel and highcombustion efficiency can be maintained.

[0054] Further, since the arrangement of this embodiment promotes apartial mixture of fuel before the fuel is injected from the end face ofan air hole, it can be expected that the fuel and air can be mixed at amuch shorter distance. Furthermore, by adjusting the length of the airhole passage, it is possible to set the conditions from almost nomixture occurring in the passage to an almost complete premixedcondition.

[0055] Moreover, in this embodiment, a proper swirling angle is given tothe central fuel nozzles 56 and the central air holes 57 to provideswirl around the combustion chamber axis. By providing a swirling angleto the corresponding air holes 57 so as to give a swirling componentaround the combustion chamber axis, the stable recirculation area byswirl is formed in the air fuel mixture flow including central fuel,thereby stabilizing the flame.

[0056] Furthermore, this embodiment can be expected to be greatlyeffective for various load conditions for a gas turbine. Various loadconditions for a gas turbine can be handled by adjusting a fuel flowrate using control valves 53 a and 54 a shown in FIG. 1.

[0057] That is, under the condition of a small gas turbine load, thefuel flow rate to the total air volume is small. In this case, bysupplying central fuel 53 only, the fuel concentration level in thecentral area can be maintained to be higher than the level required forthe stable flame being formed. Further, under the condition of a largegas turbine load, by supplying both central fuel 53 and surrounding fuel54, lean low NOx combustion can be performed as a whole. Furthermore,under the condition of an intermediate load, operation similarly todiffusing combustion which uses ambient air for combustion is possibleby setting the equivalence ratio of the central fuel 53 volume to theair volume flown from the air holes 57 at a value of over 1.

[0058] Thus, according to various gas turbine loads, it is possible tocontribute to the flame stabilization and low NOx combustion.

[0059] As described above, by arranging a coaxial jet in which the airflow envelopes the fuel, the fuel flows into the combustion chamber,mixes with an ambient coaxial air flow to become a premixed air fuelmixture having a proper stoichiometric mixture ratio, and then comes incontact with a high-temperature gas and starts to burn. Accordingly, lowNOx combustion equivalent to lean premixed combustion is possible. Atthis time, the section which corresponds to a premixing tube of aconventional premixing combustor is extremely short.

[0060] Furthermore, the fuel concentration becomes almost zero in thevicinity of the wall surface, which keeps the potential of burnoutcaused by flash back very low.

[0061] As described above, this embodiment can provide a gas turbinecombustor having low level NOx emission and good combustion stabilityand an operating method thereof.

[0062] Second Embodiment

[0063] FIGS. 5(a) and 5(b) show the detail of the nozzle portion of asecond embodiment. In this embodiment, there is a single fuel systemwhich is not partitioned into a central portion and a surroundingportion. Further, a swirling angle is not given to the nozzles in thecentral portion and the combustion air holes. This embodiment allows thenozzle structure to be simplified in cases where the combustionstability does not matter much according to operational reason or theshape of the fuel.

[0064] Third Embodiment

[0065] FIGS. 6(a) and 6(b) show a third embodiment. This embodiment isarranged such that a plurality of nozzles of a second embodiment shownin FIG. 5 are combined to form a single combustor. That is, a pluralityof modules, each consisting of fuel nozzles and air holes, are combinedto form a single combustor.

[0066] As described in a first embodiment, such an arrangement canprovide a plurality of fuel systems so as to flexibly cope with changesof turbine loads and also can easily provide different capacity per onecombustor by increasing or decreasing the number of nozzles.

[0067] Fourth Embodiment

[0068] FIGS. 7(a) and 7(b) show a fourth embodiment. This embodiment isbasically the same as a second embodiment, however, the difference isthat a swirling component is given to a coaxial jet itself by an airswirler 58.

[0069] This arrangement promotes mixture of each coaxial jet, whichmakes more uniform low NOx combustion possible. The structure of thefuel nozzle which gives a swirling component to a fuel jet can alsopromote mixture.

[0070] Fifth Embodiment

[0071] FIGS. 8(a) and 8(b) show a fifth embodiment. The difference ofthis embodiment is that the nozzle mounted to the central axis of athird embodiment is replaced with a conventional diffusing burner 61which comprises air swirlers 63 and fuel nozzle holes 62 which intersectwith the swirlers, respectively.

[0072] By using a conventional diffusing combustion burner for startup,increasing velocity, and partial loading in this arrangement, it isconsidered that this embodiment is advantageous when the startingstability is a major subject.

[0073] Sixth Embodiment

[0074] FIGS. 9(a) and 9(b) show a sixth embodiment. This embodiment hasa liquid fuel nozzle 68 and a spray air nozzle 69 in the diffusingburner 61 according to the embodiment shown in FIGS. 8(a) and 8(b) sothat liquid fuel 66 can be atomized by spray air 65 thereby handlingliquid fuel combustion. Although, from the aspect of low level NOxemission, not much can be expected from this embodiment, this embodimentprovides a combustor that can flexibly operate depending on the fuelsupply condition.

[0075] Seventh Embodiment

[0076]FIG. 10 shows a seventh embodiment. This embodiment provides anauxiliary fuel supply system 71, a header 72, and a nozzle 73 on thedownstream side of the combustor in addition to a first embodiment shownin FIG. 1 and FIGS. 4(a) and 4(b). Fuel injected from a nozzle 73 flowsinto a combustion chamber as a coaxial jet through an air hole 74, andcombustion reaction is promoted by a high-temperature gas flowing out ofthe upstream side.

[0077] Although such an arrangement makes the structure complicated, itis possible to provide a low NOx combustor which can more flexiblyrespond to the load.

[0078] Eighth Embodiment

[0079]FIG. 11 shows an eighth embodiment. In this embodiment, each fuelnozzle of the embodiment shown in FIGS. 5(a) and 5(b) is made doublestructured so that liquid fuel 66 is supplied to an inner liquid-fuelnozzle 68 and spray air 65 is supplied to an outer nozzle 81. Thisarrangement allows a large number of coaxial jets to be formed whenliquid fuel 66 is used, thereby realizing low NOx combustion where thereis very little potential of flash back.

[0080] Furthermore, it can also function as a low NOx combustor forgaseous fuel by stopping the supply of liquid fuel and supplying gaseousfuel instead of spray air. Thus, it is capable of providing a combustorthat can handle both liquid and gaseous fuel.

[0081] As described above, by making a part of or all of the fuelnozzles double structured so that spraying of liquid fuel and gaseousfuel can be switched or combined, it is possible to handle both liquidand gaseous fuel.

[0082] Thus, according to the above-mentioned embodiment, by arranging alarge number of coaxial jets in which the air flow envelopes the fuel,the fuel flows into the combustion chamber, mixes with an ambientcoaxial air flow to become a premixed air fuel mixture having a properstoichiometric mixture ratio, and then comes in contact with ahigh-temperature gas and starts to burn. Accordingly, low NOx combustionequivalent to lean premixed combustion is possible. At this time, thesection which corresponds to a premixing tube of a conventionalpremixing combustor is extremely short, and the fuel concentrationbecomes almost zero in the vicinity of the wall surface, which keeps thepotential of burnout caused by flash back very low.

[0083] This embodiment can provide a gas turbine combustor having lowlevel NOx emission and good combustion stability and an operating methodthereof.

[0084] Ninth Embodiment

[0085]FIG. 12 is a sectional view of a part of the fuel nozzle 55 and acombustion air hole 52 arranged approximately coaxially. The combustionair hole 52 is provided at a downstream side of the fuel nozzle 55 withrespect to a fuel jet flow, that is, a premixing flow passage is formedat the downstream side of the fuel jet of the fuel nozzle 55. The size(flow passage cross-sectional area) of the combustion air hole 52 isbetter to be larger than a cross-sectional area of a fuel jet hole ofthe fuel nozzle 55. In the present embodiment, the diameter (premixingflow passage diameter area) of the combustion air hole 52 is larger thanthe fuel injection hole diameter (area) of the fuel nozzle 55. Fuel isjetted from the fuel nozzle 55 through the premixing flow passage whileair flows through the premixing flow passage, whereby the fuel and airbecome a coaxial jet flow. In this case, it is desirable that the fuelfrom the fuel nozzle 55 is jetted toward a radially central portion ofan inlet of the combustion air hole 52 and a good coaxial jet flow isformed. Further, in the case of the present embodiment, a fuelconcentration distribution at a downstream side of an air outlet issymmetric with respect to a center of the coaxial flow as shown in FIG.12, and the fuel and air rapidly mix with each other and the mixturebecome uniform at the fuel and air run downstream. Thereby, a low NOxperformance equivalent to a conventional premixing combustion system isrealized by a short premixing distance as compared with the conventionalpremixing combustion system.

[0086] Further, FIG. 13a and FIG. 13b each show an example that the axisof the combustion air hole 52 is inclined at an angle θ° against thefuel jet axis of the fuel nozzle 55. The combustion air hole 52 isarranged to be coaxial in the vicinity of an inlet thereof but to beinclined against the fuel jet direction. In the case of such anarrangement, a distribution of fuel concentration in a place downstreamof the air outlet is asymmetric with respect to the air jet flow axis asshown in FIG. 13a. The fuel and air becomes mixed and uniform as thefuel air run downstream, however the asymmetry is not completelydisappear and a concentration difference exists. For example, forcoaxial jet holes near the radial center of a burner or combustor formedof a aggregation of a plurality of coaxial jet holes, as shown in FIG.13b, it is considered to positively utilize such a deviation between thefuel jet axis and the air hole axis. That is, in the present embodiment,the burner is constructed so that the above-mentioned inclination (θ°)is provided for the combustion air holes around a flame stabilizingregion which is around a radially central portion of the burner, but theinclination is not provided (θ°=0) for the combustion air holes in theother region than the central portion, whereby it is possible to keepthe fuel concentration of the flame stabilizing region relatively richand make the stability of flame stronger. In the present embodiment, byproviding only the combustion air holes with an angle not parallel tothe axis of the burner such as swirling angle while employing a straightjet hole having no swirling angle or no inward or outward angle, it ispossible to provide premixed gas with a swirling angle or an inward oroutward angle by a relatively simple construction and it is possible toset a premixed gas flow according to the construction and object of theburner, which is excellent.

[0087] Next, FIG. 14 is an example in which an axial position of thefuel jet hole and combustion air hole is the same as in FIG. 12 and apositional deviation (d) in a radial direction is intentionally settherebetween. By the positional deviation, a fuel concentrationdifference becomes an asymmetric distribution with respect to an axis ofair jet flow, whereby it is possible to positively generate a differencein fuel concentration and improve combustion characteristics such ascombustion stability.

[0088] In the present embodiment as mentioned above, fuel from the fuelnozzle 55 flows along an approximately central portion of premixed gasin the premixing flow passage. Further, the burner is constructed sothat air from an outer peripheral side of the fuel nozzle 55 flows inthe premixing flow passage along an outer peripheral side thereof.Therefore, the air flows at the outer peripheral side of the fuel flowalong the fuel flow in the premixing flow passage, and the fuel and airflows become approximately coaxial. By providing a plurality of nozzlesof such formation, it is possible to promote mixing of fuel and air andrealize stable combustion by a simple construction.

[0089] Further, (a) and (b) of FIG. 15 show an example of a shortpremixing distance L and an example of long premixing distance,respectively. The mixing by rapid expansion after being going out of thecombustion air hole is predominant, and it is considered that aninfluence of the premixing distance L on the uniformity of mixing andlow NOx performance is not so large. As shown in (a) of FIG. 15, even ifa member forming the combustion air hole is made thin thereby to makethe premixing distance L short, it is considered that the low NOxperformance is sufficiently secured. On the other hand, saving of thematerial of the member forming therein the air hole and a work cost ofperforation of the air hole can be expected, whereby it is advantage forcost reduction. (b) of FIG. 15 shows an example in which the premixingdistance L is sufficiently long. It can be expected that fuel and airare sufficiently mixed within the mixing flow passage, and it ispossible to provide a burner excellent in low NOx performance. Further,in the case where swirling components are provided by providing aninclination angle for the combustion air hole and a function such asgiving an inward or outward deviation angle is provided, also, themixing distance L is preferable to be about several times as large asthe air hole diameter.

[0090] (c) and (d) of FIG. 15 show example in which axial distances Gbetween an end of the fuel jet hole and an inlet of the air hole aredifferent. (C) of FIG. 15 shows an example that the axial distance G islarge, the example is advantageous in uniform mixing and low NOxperformance because a substantial premixing distance can be made long.Further, since the length of the fuel nozzle can be made short, amanufacturing performance of the fuel nozzle is increased and costreduction is possible. On the other hand, (d) of FIG. 15 is an exampleof arrangement in which a premixing flow passage is formed at adownstream side of the fuel nozzle 55 and the axial distance G is minus,that is, the fuel jet hole projects into inside of the air hole. By sucharrangement, potential of backfire can be reduced greatly, and thearrangement is considered to be effective in the case where fuel ofexcellent ignitability such as dimethylether (DME) is burnt with low NOxemission.

[0091] (e) and (f) of FIG. 15 show an example in which the diameter D ofthe air hole is small and an example in which it is large, respectively.In the case of (e) of FIG. 15 in which the diameter D is made small andthe number of the air holes are increased thereby, fuel and air aredispersed finely and supplied, so that they are mixed well and uniformin a short distance and it is suited for the case where a lower NOxperformance is considered important. In the case where the diameter D ofthe air hole is made large and the number of the air holes is made lessas shown in (f) of FIG. 15, the mixing distance is necessary to be longand the uniformity of mixing is lost a little, so that the low NOxperformance is a little inferior to the above, however, it isadvantageous in the case where cost reduction is considered importantbecause working steps are reduced and the required manufacturingprecision is not so high.

[0092] Tenth Embodiment

[0093]FIG. 16a shows another embodiment. In the embodiment describedabove, the coaxial air holes 52 within a burner plane are arrangedcoaxially and dispersively, however, basic characteristics are not losteven in lattice or ziqzaq arrangement of the air holes. FIG. 16a showsan example of such an arrangement as mentioned above. In the case ofsuch an arrangement, axial position at which flame is formed is within asection of the liner and substantially the same floating flames aregenerated although it differs according to an average velocity on aburner liner. It is better on manufacturing because of simpleconstruction, however, in some cases, it is insufficient in flamestability. FIG. 16b shows an example for such a case, in which a regionin which pitches between air holes 52 are the same and areas of the airholes each are smaller, a region of no air hole or larger pitches, orthe like are provided thereby to form a low flow rate portion (low speedportion) and a circulation flow region, whereby flames are stabilized inthose regions. With such a construction, potential of backfire is low,and it is possible to provide a burner with both low NOx performance andcombustion stability.

[0094]FIG. 17 shows an example of experimental results about arelationship between premixing distance L and NOx emission amount in therepresent invention. Although complete premixing combustion that fueland air are mixed completely and then burnt is necessary to use apremixing device with sufficiently long mixing distance or largepressure loss, a NOx emission amount by the complete premixingcombustion is very small (a point A in FIG. 17). On the other hand, in apractical premixing device construction which is constructed byarranging a plurality of fuel nozzles in an annular premixing flowpassage, NOx emission amount increases in an approximately reverseproportion to the premixing distance L, and an example of NOx emissionby such a premixing device is shown by a point B.

[0095] On the contrary, in the present invention, a relationship betweenpremixing distance and NOx emission amount in one embodiment of thepresent invention in which the nozzles and air holes are arranged so asto be a plurality of coaxial jet flows is as shown by a point C in FIG.17, low NOx performance equivalent to that by a conventional premixingdevice can be achieved by a premixing distance equal to or smaller than{fraction (1/20)} times as long as the premixing distance in theconventional construction although the low NOx performance is less thanthe perfect premixing combustion.

What is claimed is:
 1. A gas turbine combustor having a combustionchamber into which fuel and air are supplied, wherein the fuel and theair are supplied into said combustion chamber as a plurality of coaxialjets.
 2. A gas turbine combustor comprising a fuel nozzle for injectingfuel into a combustion chamber and an air hole for injecting air intosaid combustion chamber, wherein the fuel nozzle and the air hole aredisposed so that the fuel and the air are injected into said combustionchamber as a plurality of coaxial jets.
 3. A gas turbine combustorcomprising a fuel nozzle, an air hole and a combustion chamber, whereinfuel and air are injected into said combustion chamber as a large numberof small diameter coaxial jets.
 4. A gas turbine combustor according toclaim 3, wherein a fuel hole of the fuel nozzle is disposed coaxially oralmost coaxially with the air hole, a fuel jet being injected toward thevicinity of the center of the air hole inlet, and a fuel jet and acircular flow of the air enveloping the fuel jet being injected into thecombustion chamber as a coaxial jet from an outlet of the air hole.
 5. Agas turbine combustor according to claim 4, wherein a large number ofthe fuel nozzles are partitioned into a plurality of fuel supply systemsand a control system is provided so as to individually control the flowrate of each fuel according to the load on the gas turbine.
 6. A gasturbine combustor according to claim 5, wherein, a swirling angle whichprovides a swirling component around the axis of the combustor is givento a part of or all of the fuel nozzles among a large number of the fuelnozzles and corresponding air holes.
 7. A gas turbine combustoraccording to claim 5, wherein a fuel hole of the fuel nozzle is disposedcoaxially or almost coaxially with the air hole, a fuel jet beinginjected toward the vicinity of the center of the air hole inlet, and afuel jet and an circular flow of the air enveloping the fuel jet beinginjected into the combustion chamber as a coaxial jet from an outlet ofthe air hole, and a plurality of modules, each module consisting of thefuel nozzle and the air hole, are combined to form a combustor.
 8. A gasturbine combustor according to any one of claims 3 through 7, wherein amechanism which provides each air hole or fuel nozzle with a swirlingcomponent around each axis.
 9. A gas turbine combustor according toclaim 3, wherein a part of or all of the fuel nozzles are doublestructured so that spraying of liquid fuel and gaseous fuel can beswitched or combined.
 10. A method of operating a gas turbine combustorhaving a combustion chamber into which fuel and air are supplied,wherein the fuel and the air are supplied into said combustion chamberas a plurality of coaxial jets.
 11. A method of operating a gas turbinecombustor having a combustion chamber into which fuel and air aresupplied, wherein a plurality of fuel nozzles for injecting the fuel areprovided, the fuel nozzles being partitioned into a plurality of fuelsupply systems, the flow rate of each fuel being individually controlledaccording to the load on the gas turbine, and the fuel and the air beingsupplied as a plurality of coaxial jets.